I'm a bit of a late-comer, but I'd like to address an issue from earlier. I'll get to alignments in a moment...
is cuttin down a forest (nature) to replace it with crops (nature) a bad thing to a druid?
Cultivated areas are NOT a viable ecosystem, therefore they are NOT part of nature in the traditional sense. So destroying a forest(nature) to plant crops(not nature) would be a bad thing to a D&D druid (and probably to a "real" one as well, to a point).
I'm having a hard time trying to rectify a modern concept of environmentalism with a medieval/ancient world. Most medieval/ancient worlds didnt have the pressing concerns that we have, because they didnt' have the vast population nor the technology to for vast actions.
Modern environmentalism has
nothing to do with druids. As far as I've been able to piece together from a LOT of reading on the subject, Druids, like most Native Americans, were aware of the symbiotic relationships going on all around them. They showed respect for the animals and plants that were used to sustain human life. Also like Native Americans, the Celts had a low-impact lifestyle until Christianity arrived. Emphasis on low-yield crops, gathering, and hunting. Often, mixed crops were planted in the same area. This helps prevent soil depletion, though I doubt the Celts knew that,
per se. They had significantly less cultivation in general than city-bound civilizations. At any rate, large scale agriculture is only necessary once you start to encourage clustering of people into large populations. The Celts did not. They tended to be spread out over large areas, as was necessary for their low-impact lifestyle.
Ultimately, my impression is that druids would encourage small communities, small population, and sustainable, small-scale agriculture. Really, they were protectors of the Celtic people and way of life, not the protectors of nature they were made out to be. Of course, unlike the people who did the writing (Romans & Christians), they understood that protecting nature was
part of protecting their way of life. And since nature was the abode of "barbarians" and"pagans", labeling the druids as such was convenient.
For game flavor reasons, "protector of nature" is probably better than "holy man of the Celtic people" though.
If you accept the D&D assertion that nature is Neutral by default, then I can't argue with Nightfall. Those are the "acceptable" alignments.
Personally, I always felt that druids were definitively Good, as they give of themselves to protect a lifestyle (which benefits their people) and nature (which ultimately benefits all creatures). An evil druid is a contradiction in terms, IMO. I always thought of them as Pragmatic Good. They take the long view of protecting the support system for life. Their goal is safeguarding all life, and they are Natural Selection in action, culling the weak and aberrant from nature, and reigning in those who would do lasting harm to the ecosystem (whether they fully understand the concept of an "ecosystem" or not).